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AIRCRAFT TRAINING APPARATUS FOR smuuvrmc THE PROPELLER SYSTEM OFTURBO-PROPELLER AIRCRAFT Original Filed Dec. 5, 1957 5 Sheets-Sheet 1 WMW ET 5 .1

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4- I250 NORMAL H6} IN A; F n 7 mourn". EEILBUS n: ATE 96 HIE: ATTORNEY1963 R. H. soonwm AIRCRAFT TRAINING APPARATUS FOR SIMULATING THEPROPELLER SYSTEM OF TURBO-PROPELLER AIRCRAFT Original Filed Dec. 5, 19575 Sheefs-Sheet 2 o8 h rap? Q5 INVENTOR. RDSCDE H. EDDDWIN (Qwflzwm.

HIEI ATTORNEY R. H. eoonwm Re. 25,325 AIRCRAFT TRAINING APPARATUS FORSIMULATING THE PROPELLER Jan. 29, 1963 SYSTEM OF TURBO-PROPELLERAIRCRAFT Original Filed Dec. 5, 1957 5 Sheets-Sheet 3 oFEn :b omxLou 50ov.56:

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INVENTOR. RUEECIE H. EDCIDWIN W Z PM H15 ATTDRNEY Jan. 29, 1963 R. H.GOODWIN AIRCRAFT TRAINING APPARATUS FOR SIMULATING THE PROPELLER SYSTEMOF TURBO-PROPELLER AIRCRAFT Original Filed Dec. 5, 1957 5 Sheets-Sheet 4INVENTOR.

RESCUE H. EUUDWIN min 5.5.

HIE! ATTORNEY Jan. 29, 1963 R. H. GOODWIN AIRCRAFT TRAINING APPARATUSFOR SIMULATING THE PROPELLER SYSTEM OF TURBO-PROPELLER AIRCRAFT 5, 19575 Sheets-Sheet 5 Original Filed Dec.

udnzumr 2mm nz INVENTOR. I RUfiF UE H. EIJDDWIN HIE ATTORNEY UnitedStates Patent AIRCRAFT TRAINHNG- AEE ARATUS 130R Silt EU- LATING THEPRGFELLER SYSTEM OF TU LZEU- PRGPELLER All iCRAFT Roscoe H. Goodwin,Allendale, N .1, assignor to Curtiss- Wright Corporation, a corporationof Deiaware Original No. 2,975 533, dated Apr. 18, 1%1, Eer. No.700,830, Dec. 5, 1957. Application for reissue lune 12, 1962, Ser. No.$53,689

24 Ciaims. (Cl. 35-12) Matter enclosed in heavy brackets E: 1 appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to ground apparatus for training aircraftpersonnel, and in particular to apparatus for simulating the operationand control of turbine driven propellers of so-called turbo-propaircraft.

Simulation of the operation of constant speed, variable pitch aircraftpropellers driven by reciprocating piston engines is disclosed by theprior art, an example being US. Patent No. 2,788,589 granted April 16,1957 to Robert G. Stern. The simulation however of turbinepropellersystems has not heretofore to the best of my knowledge beensatisfactorily accomplished. This simulation involves unique and quitedifferent problems due to the radical differences between the high speedgas turbine and the reciprocating engine with relation to the drive of avariable pitch propeller. These diiferences involve the operatingcharacteristics of the gas turbine and practical considerations such asthe comparatively high inertia of the turbine assembly rotating at veryhigh speed in its relation to the propeller blade angle control.

A principal object of the invention is new and improved simulatingapparatus that is efficient and realistic in representing various phasesof operation and control of the propeller system of turbo-propelleraircraft, and that is valuable in the ground training of aircraftpersonnel.

The invention will be more fully set forth in the following descriptionreferring to the accompanying drawings, and the features of novelty willbe pointed out with particularity in the claims annexed to and forming apart of this specification.

Referring to the drawings:

FIG. 1 is a diagrammatic illustration of the principal simulatedpropeller system controls and servo units in their relation to systemrelays used in the simulating system of the present invention;

FIG. 1A diagrammatically illustrates the control system for the startvalve relay used in the simulated turbine starting operation;

FIG. 2 is a similar illustration of the circuitry for producing theautomatic governing correction signal, controlling the propellerunderspeed relay and synchronizing from a master control engine theremaining engines;

FIG. 2A graphically illustrates the method of applying the synchronizingsignal to the simulated slave engines of FIG. 2;

FIG. 3 diagrammatically illustrates the simulated propeller blade anglecomputing system;

FIG. 4 is a similar illustration of the computing apparatus forproducing the simulated propeller load signal P for the simulating.system;

=FlG. 5 diagrammatically illustrates the computing apparatus of thesimulated turbine rpm. system, and

FIG. 5A graphically illustrates the relation between the simulatedengine torque and the torque function signal for a given value ofpropeller load as applied to the rpm. servo of FIG. 5.

The present invention although not limited thereto,

"ice

is shown by way of example as applied to the simulation of a specificturbine driven propeller having in part a hydraulic control system,namely that of the Air Force C-A aircraft; however it will be understoodthat the invention is also applicable as well to the simulation ofelectrical or other control systems for the propeller. In order to avoidduplication of disclosure, simulation of the system of a singlepropeller unit of the aircraft is described in detail, it being ofcourse understood that this system may be duplicated in obvious mannerfor a multiple propeller system of this character.

For a better understanding of the invention the aircraft equipmentherein simulated in part will first be briefly described. The propulsionand power units of the modern turbo pro-p aircraft comprise a variablepitch, constant speed propeller that is driven through reduction gearingby a high speed gas turbine rotating at optimum speed, say about 13,000rpm. As more or less fuel is fed to the turbine to meet powerrequirements, the speed of the turbine-propeller combination ismaintained constant by automatic adjustment of the propeller blade angleso that the power absorbed by the propeller matches the turbine power.In the pilots compartment or cockpit of the aircraft is a set of primarycontrols for each engine, each set including a power lever, conditionlever and so-called panic handle all operable by the pilot. In addition,there is a master engine synchronizing. switch and a set of electronicpropeller governor switches. During normal flight operation the pilot isconcerned only with the power lever which is movable through acontinuous angle defining two distinct sectors or ranges of operation,namely, (1) a so-callcd BETA range (usually used for ground operation)wherein the power lever di-.

rectly controls the propeller blade angle, starting with advance of thelever from full reverse pitch to about 9 positive pit-ch, and (2) anAUTOMATEC GOVERNING uange wherein the power lever controls the fuelsupply to the turbine, and the propeller pitch is automatically adjustedby the regulator and acceleuation-sensitive means so as to maintainconstant r.p.m. Thus the power lever, starting from the full reversepitch position, may be advanced through the Beta range and into theautomatic governing range up to the full or take-off (TO) powerposition, and vice versa, as conditions require.

The condition lever has four positions, namely, (1) FEATHER, wherein thepropeller can be feathered by main and auxiliary power systems uponfailure of the turbine, (2) NORMAL, wherein the usual controls used inflight and for a ground start are available, (3) AIR START, wherein theblade I ngle is gradually decreased from feather so as to drive theturbine by wiudmilliug" action preparatory to refining the turbine, and(4) GROUND STOP, wherein the fuel supply is curt-off. Supplemental tothe condition lever in the NORMAL position is a start button that isused primarily for ener-gizing the starter motor.

The panic handle is solely for Eemergy] emergency operation andoverrides all other controls. It functions to shut oif the fuel supply,discharge the CO system and feather the propeller, thus shutting downthe power system of the corresponding turbo-prop unit.

The instruments in the cockpit that the pilot relies upon with referenceto propeller control are the torque meter and the r.=p.m. meter. Thetorque meter indicates the amount of positive or negative torque at thepropeller drive shaft, i.e. positive torque as evidenced by turbinedrive of the propeller, and negative torque due to windmilling effect.The rpm. meter simply indicates the speed of the turbine. The turbopropaircraft is provided with a decoupling device between the propeller andturbine so that the drive connection is decoupled when negative torqueexceeds a predetermined critical amount; thus, by observing the torquemeter, the pilot can during an air start adjust the blade anglegradually for cranking the turbine so as not to exceed the maximumnegative torque, namely -4 8(l0 in.-lbs. and cause decoupling.Decoupling may take place following engine trial-function and prior tocomplete feathering of the propeller. Upon feathering, coupling occursautomatically so that the unit is in readiness for an air start, if suchis called for.

Synchronization incidental to multi-engine operation is accomplished byselecting one engine as the source of master speed and slaving the otherengines to the master engine. The above description covers only basicfeatures of the turbopropeller system. Other features ancillary tooperation and control of'the'propeller under various conditions will bereferred to in the following description of the simulating system.

The simulation of the gas turbine system per se which delivers torque tothe propeller constitutes a separate invention that is disclosed andclaimed in a copending application, SN. 700,407 filed December 3, 1957,by Robert F. A. Lem, now Patent 2,940,181 and assigned to the sameassignee as the present invention.

The simulating system herein described is shown by way of example as ofthe alternating current (A.C.) type (except where'D.C. voltages areexpressly indicated) although it will be understood that the system maycomprise in whole or in part well known direct current (D.C.) techniquesas desired. The system will be described in connection with itsfunctioning under the control of a pilot and/or instructor for acomplete simulated flight comprising ground start, take-off, cruisingincluding inflight conditions such as feathering due to enginemalfunction, air-start, etc, landing and engine shut down. Forconvenience in description, the various relays, etc., of the system areshown in the condition they would assume in normal flight.

GROUND START.

Referring to the drawings, the conditions requisite for ground start areas follows: the condition lever 1, FIG. 1, is set at NORMAL, the powerlever 2, FIGS; 1 and 5, is positioned for ground-idle which is withinthe indicated ground (GND) or Beta range for setting a fiat blade angleof about 0, the panic handle '3 is set at NORMAL, the master enginesynchronizing (Ma ENG SYNC) switch 4 is set at the engine No. 1 (ENG 1)position for ex ample, and the electronic propeller governor switch 5 issetat the synchronizing (SYNC) position. A number of system relays arecontrolled according to the various positions of theselevers andswitches, and in the present instance the power lever causesenergization of the Beta range relay 6 from the main relay source 151 atbus 7 through switch 11 and the relay 6 to ground. The switch 11 ispositioned to complete the circuit by the low side of the cam 12 whichis in turn connected to the power lever 2 as indicated at 13.

At this stage, simulation of firing and starting of the turbine is inorder followed by acceleration up to the ground idle speed. This isinitiated by operating a start button 14, FIG. 1A, to energize the startvalve relay 15, FIGS. 1A and 5, for simulating initial cranking of theengine. Subsequently the flame relay 16 is energized for firing theturbine. The specific circuitry for controlling the flame relay is notessential for an understanding of the present invention and is disclosedin the aforesaid copending Lem application.

The relays 15 and 16 control in a manner presently described variousA.C. input voltages or signals that operate an electrical computingservo system 17, FIG. 5, that represents turbine r.p.m. (N) which willfirst be described. The system 17 comprises a summing amplifier 18 foralgebraically summing in well-known manner the AC. input signalsvariable in magnitude and phase relation, which are fed to the amplifierinput network generally indicated at 19, and a reversiblemotor-generator combination (MG) 20 controlled by the output of theamplifier. An MG drive connection indicated at 21 operates a pluralityof potentiometers, hereinafter often referred to as pots, and camswitches, etc, including the answer pot 22, an r.p.m. switch cam 23 andan indicator 24 for representing turbine r.p.m. A specific form of MGcontrol circuitry is later described in connection with FIG. 3, althoughit will be understood that any suitable servo mechanism or system may beused in practicing the invention. It will for the present be suflicientto state that the scrvomotor is operable in speed and directionaccording to the magnitude and phase relation respectively of theresultant A.C. output signal from the N amplifier 18 so as to positionthe slider contact 22' on the pot 22, rotate cam 23 according tosimulated r.p.m. range and position the rpm. indicator 24.

Returning now to the initial starting operation, operation of the startvalve relay 15' gang-operates the relay switches 25, 26 and 27, FIG. 5,to the lower positions thereof to engage their respective b contacts.This operation of the switches 25 and 26 introduces a start signal N(ST) to the N input network 19 at terminal 28. In order to simulate thecharacteristic delay between the operation of the start valve andpick-up in turbine speed, the switch 25- through its b contact closesthe circuit of a heater element 29 for a conventional thermal time delaydevice 30. Heating of the element 29 causes closing of the thermalresponsive switch 31 on its a contact so as to complete the start signalcircuit that is energ'med by a constant voltage +E representing startertorque, the switch 25 through its b contact now being connected inseries with the thermal switch 31. This starter signal operates the Nservo system so as to move the pot slider.

22 upward from its zero grounded position and increase the derivedvoltage from source E constituting the answer voltage (-ANS) that isapplied to the-input network by lead 32. When the starter input signal+N (ST) is equalled by the oppositely phased answer signal, the input tothe N servo is zero and the servomotor is deenergized to indicateconstant rpm.

During this initial operation wherein the turbine speed is representedas increasing from zero to about 2,000 rpm. under influence of thestarter, the dynamic characteristics of the system are simulated bymeans of'a negative feedback signal from the generator of the MG unit tothe input network. The resultant feedback signal is varied according tocertain operating conditions by connecting one or more circuitsincluding the usual input proportioning resistances in parallel with thepermanently connected feedback circuit FDBK at terminal 33. One parallelcircuit FDBK connected to the input network at terminal 34 is controlled'by the socalled 9,000 rpm. relay 35 so as to ground out the shuntcircuit by switch 36 at its b contact when the relay is deenergizedi.e., the rpm. is equal to or greater than 9,000 r.p.m., and to completethe shunt circuit at the switch a contact when the relay is energized toindicate less than 9,099 rpm. Energization of the relay 35 is controlledby the N cam 23 and switch 23a. A second shunt circuit FDBK is connectedto the input network at terminal 37 by the flame relay switch 38 throughits a contact during the starting operation prior to energization of theflame relay 16. Thus, for the starting condition while the turbine speedis accelerating up to about 2,000 r.p.m., maximum negative feedback isintroduced for causing comparatively sluggish response of the servosystem in simulation of the engine starting system.

At about 2,000 r.p.m. the flame relay is energized to simulate firing ofthe turbine. The flame relay switches 38 and 39 are thereby operated totheir lower positions to engage their respective b contacts so thatswitch 38 now grounds out the second feedback shunt circuit FDBK therebydecreasing the amount of feedback. Switch 39, which formerly hadgrounded out through its a" contact the combined start (ST) and flame(FL) signal circuit N (ST, FL) connected to the input network atterminal 40, now connects this circuit in shunt with the N(ST) circuitso as to increase the combined torque signal tending to accelerate the Nservo. Acceleration of the servo now under decreased influence offeedback, continues at more rapid rate up to about 7,000 r.p.m., atwhich point the start valve relay drops out (removing the cranking inputsignal) and the turbine is represented as being sustained by the flamecondition. Specifically, as the start valve relay 15 is deenergized, theswitches 25, '26 and 27 move to their upper positions to engage theirrespective a" contacts with the result that switch now grounds out thestarter torque N (ST), switch 26 deenergizes the thermal delay device30' and switch 27 moves from its grounded position to feed to the inputnetwork at terminal 41 the main torque input signal N(P ,Q) that isderived from the potentiometer 42 operated as indicated by the torque(Q) servo 43. The pot 42 is energized at its terminals by oppositelyphased voltages representing propeller load (P and is designed so thatthe derived signal voltage at slider 4-2 represents a function of torqueaccording to the characteristic curve of FIG. 6 [this] which is based onthe relationship.

for given values of blade angle B true airspeed V and air density p.

This torque signal is the primary signal for controlling the N servoduring the normal, fired condition of the turbine after the startingperiod. In order to simulate reversal of this characteristic signal inthe negative quadrant according to FIG. 6, two oppositely phased Pvoltages are alternatively applied to the slider 42' through aproportioning resistance 42a and switch 42b when the torque passesthrough zero as indicated by the grounded position of the pot 4 2. Theswitch 42b is operated by the torque relay 4321 that is in turncontrolled by the torque servo cam 43b and switch 43c as shown. Thederivation of the P signal will be later described in connection withFIG. 4.

The energizing circuits for the torque servo system 43 are not disclosedherein but are disclosed in the aforesaid copending Lem applicationdirected to the simulated gas turbine system. It is sufi'icient forpresent purposes to state that the torque servo operates, according tothe computed engine torque, between positive and negative torque limitsas indicated.

An additional signal representing the airspeed effect on r.p.m., bothfor normal and windmilling conditions is t applied to the input networkcircuit AN(N, V at terminal 43. This signal is derived from pot 44- atslider 44' of the blade angle (B servo system 4-5 and is a function ofblade angle and true airspeed (V The energizing circuits for the B servoare described later in connection with FIG. 3. The pot 44 is energizedat its terminals 44a and 44b respectively by voltages representingairspeed factors and is designed so as to produce a suitablecharacteristic signal for modifying the operation of the N servo. Thevoltages for energizing the pct 44 are in turn derived from othercircuitry as later described.

From the aforesaid 7,000 r.p.m. point, the N servo now under theinfluence of the torque signal at terminal 41 accelerates more rapidlyup to its ground idle speed of about 13,400 r.p.m. as the relay isdeenergized and its switch as grounds out the remaining shunt feedbackcircuit FDBK As desired, a simulated trouble signal of alternate sensemay be introduced at any time by the instructor in the input networkcircuit N(INST) at terminal 46 by means of a pot 47 that is controlledby the instructors lever 48. The N servo may thus be fed trouble signalseither to increase or decrease r.p.m.

As previously indicated the N servo controls according to r.p.m. limitsvarious phases of the ground-start up to ground idle r.p.m. This controlis interrelated with the condition of the start valve relay and is shownby FIG. 1A. When the starter button 14 is pushed so as to initiate theground start operation, its contact 50, which is electrically connectedto the voltage source E at the bus 7, engages the contacts 51 and 52which are connected respectively to the a contact of the 13,000 r.p.m.switch 53, and the coil of the latching relay 545. The latching relay isconnected at its opposite terminal to a switch 55 of the 7,000 r.p.m.relay 56 that has its ground circuit completed by the N servo cam 57 andswitch 58 when r.p.m. is less than 7,000. In this condition whichprevails at start, the switch 55 engages its a contact to complete theground circuit for the latching relay 54 which is now energized from thebus and holds the contact in circuit through suitable means indicated at54a. Accordingly, the starter button is latched-in as long as r.p.m. isless than 7,000.

The 7,000 r.p.m. relay which is energized due to the position of the Ncam 57 prior to operation of the starter button, also closes switch 59on its a contact that is in circuit with the start valve relay 15. Asthe 13,000 r.p.m. relay 60 is energized when r.p.m. is less than 13,000so as to close its switch 53 on its a contact, it will be apparent thatthe start valve relay 15 is now energized from the bus through thestarter contact 50 and seriesconnected switches 53 and 59. The groundcircuit of relay 15 may also be controlled as desired by an instructorsswitch 61 to represent the availability of pneumatic pressure foroperating the starter.

Energization of the start valve relay 15 represents opening of the startvalve for cranking the turbine. When the simulated turbine speed attains7,000 r.p.m., the N cam 57 cuts-out the 7,000 r.p.m. relay and theswitches 59 and drop to their lower or b contact positions, therebydeenergizing the start valve relay 15 as well as the latching relay 54which permits the starter button to return to its original position.

Under certain conditions, the start valve relay may be deenergized whenturbine speed is still under 7,000 r.p.m. and the start button isdepressed. This is accomplished by the 13,000 r.p.m. relay that iscontrolled by the panic handle switch 62 and the N cam 6-3. The camcompletes the ground circuit of the relay when r.p.m. is less than13,000 and the switch 62 connects with the bus "7 through the circuitbreaker 64 in the normal position. Thus, the pilot may at any time,either by throwing the panic handle to PANIC position or by pulling theEmergency Shutofif Valve circuit breaker 64, deenergize the relay thuscausing the switch 53 to drop out and deenergize the start valve relay.For present purposes, the operating limit assigned to the 13,000 r.p.m.relay is arbitrary as this relay also is used for other purposes in theengine system of the aforesaid copending Lem application.

Immediately upon deenergization of the start valve relay 15*, FIG. 5,the relay switch 27 moves to its a contact position and brings in thetorque signal from pot 4 2 which as previously described is a functionof propeller load (P The P signal which energizes the pot 42 is derivedaccording to the following relationship:

where V is true airspeed, p is air density and B is propeller bladeangle.

Referring to FIG. 4, servo circuitry for computing this equationaccording to propeller characteristic data includes a plurality ofinterconnected electrical systems representing primarily the respectivefactors V p and B The V servo system is operable between arbitrarylimits of speed, such as from zero to 400 knots and controls a signalpot 126 for deriving the signal f(V Circuitry for controlling the Vservo is disclosed for example, in Patent No. 2,731,737 granted January24, 1956 to R. G. Stern. This V signal is fed to the terminal 44b of pot44, FIG. 5, and also to the input of an amplifier 127 representing theeffect of airspeed on propeller RPM (RPM The output of this amplifier isfed to a transformer 128, the secondary winding 129 of which is groundedat its midportion for producing RPM signals of opposite sense at itsterminals. One of these signals is fed to the terminal 44a of pot 4-4,FIG. 5, and another is fed by lead 129 to the pot 131 of the servosystem 130 for producing a signal representing RPM (l/ K). Circuitry forcontrolling the p servo is disclosed for example in Patent No. 2,788,589granted April 16, 1957 to R. G. Stern. The pot 131 is suitably designedas indicated for producing a signal corresponding to the reciprocal ofthe square root of the constant K being represented by the offset fromzero of the energizing tap at 131. This signal is in turn fed to theinput of summing amplifier 132 together with the RPM signal from theservo transformer 128. The resultant of these signals at the output ofthe amplifier 132 is represented by a signal voltage RPM /V; at theterminal of the secondary winding 133 of the output transformer 134.This signal is used in the direct computation of P as presentlydescribed.

Referring again to the p servo 139, this servo controls through aconnection 135 a function pot 136 for producing a signal at the slider136. This signal is fed, together with a constant voltage signal +Erepresenting the constant K, to a summingamplifier 137, the output ofwhich appears as a signal on the secondary winding 138 of the outputtransformer 139. This signal energizes the function pot 140 of the Bservo system 45 and the signal derived at the slider 140 represents theeffects of air density and blade angle on propeller load. This signal isin turn fed to the P computing amplifier 141. A second function pot 142of the B system is connected as indicated by lead 143 to the secondarywinding 133 of transformer 134 so as to b e energized by the abovedescribed signal RPMv /Vp. The derived signal at slider 142 which is fedto the P amplifier represents the effects of RPM p and B on propellerload, P The resultant signal appearing at the output of amplifier 141represents P and is fed to the output transformer 144 having a secondarywinding 245 that is grounded at its mid-portion so as to produce Psignals of opposite sense at its terminals. These P signals are used forenergizing the circuitry of the function potentiometer 42 of FIG. 5 asabove described.

TAKE-OFF With the turbine now running at ground idle the aircraft isready for take-off. This operation is initiated by advancing the powerlever through the Beta and automatic governing ranges to the maximum ortakeof (T0) power position. During this movement the propeller pitch isfirst increased by the power lever up to about 9 of positive pitch,after which the blade angle control is transferred to the automaticgoverning system for producing maximum propeller thrust at constantturbine speed. In the simulation of this system, the power lever 2, FIG.3, is advanced as above indicated to the T0 position. During the initialmovement of the power lever the blade angle (B servo system 45 isdirectly under the control of the power lever as long as. it is in theBeta range. Specifically, the power lever 2 controls as indicated, theslider 65' of a potentiometer 65 that is energized by a constant voltage+E so that the derived'voltage at the slider represents the blade anglecorresponding to the power lever position. This voltage constitutes themain input signal for the B system when operating in the Beta range andis applied through the Beta range relay switch 66 and its b contact tothe input network of the B system at terminal 68.

The Beta range relay 6 is energized, as previously de scribed in FIG. 1,when the power lever is in the Beta range so that the Beta relayswitches 66, 67 and 69 now are at their lower b contact positions. Thusa power lever (PL) signal is applied to the B input network by theswitch 66, an F1 (flight idle) stop signal is grounded out by the switch67 and the answer pot 70 of the 13 servo is connected by the switch 69to the input network for operating the B system as a position servo inwellknown manner, according to the PL signal from pot 65.

In the deenergized position of the Beta range relay the switches 66, 67and 69 are at their upper or a contact positions whereby the PL andanswer signals are grounded-out. A constant FI stop signal +E may be fedthrough switch 67 to the B system according to the position of theautomatic governing (AUTO) relay switch 71 of the AUTO relay 72 whichwill be later described. This relay also controls the main input to theB system for automatic governing control, is. the propeller under-speed(PU) signal.

The B servo system which is in general typical of the servo motorsystems used throughout the present simulating system and which isconventional alternating current two-phase servomotor system, will bebriefly described. The servo system comprises a servo amplifier 75 thatis energized at its input side from the aforesaid input network andfunctions as a summing amplifier of well-known type as described inconnection with the N servo amplifier 18, FIG. 5. The amplifierresultant signal, which may vary in magnitude and phase relation withrespect to a reference voltage, energizes the control winding 76 of aservomotor 77 of the well-known two-phase type. The second or referencewinding 78 of the servomotor is energized by a constant referencevoltage e that is dephased with respect to the control voltage onwinding 76. The operation of this type of motor is well-known, therotation being in onedirection when the control and reference voltagesin the respective phase windings have the same instantaneous polarity,and in the opposite direction when the instantaneous polarity of thecontrol voltage is reversed with respect to the reference voltage, therateof rotation in both cases depending on the magnitude of the controlvoltage. The motor control circuitry is shown in elementary form in theinterest of clearness and it will be understood that other known servosystems may be used according to specific requirements.

The servomotor 77 drives a two-phase feedback generator 79 also having areference phase winding 81] that is energized by a 90 dephased referencevoltage c and a second phase winding 81 for generating a velocityfeedback voltage FDBK that is fed by lead 82 to the input network atterminal 83 for purposes of speed response control. The negativefeedback signal which may vary 1n magnitude and polarity according tothe speed and direction of rotation of the generator, represents rate ofchange of blade angle and may be modified as hereinafter described torepresent different speedresponse characteristics of the B system. Theservomotor also serves to gang-operate through the gear reducer 84 andsuitable mechanical connections indicated at 85, one or more pots,switching cams, etc. In the present instance the slider 7d of pct 70 ispositioned so as to derive an answer voltage from the pct 70 that is fedby line 86 to the b contact of the Beta range switch 69 in the inputnetwork. Accordingly when the Beta range relay is energized, the answerpot '70 is connected to the input network for causing the B system tofunction as a position servo; when the Beta range relay is deenergized,the answer signal is cut-out, as is also the P signal from pot 65, andthe B system then functions primarily as an integrating servo in. theautomatic governing range under influence of the main propellerunder-speed (PU) signal at the input terminal 87.

The PU signal is derived by the circuitry later described in FIG. 2 andis cut-in by the AUTO relay switch 88 at its a contact when the AUTOrelay '72 is energized, thus indicating that the system is in theautomatic governing range. The switch 88 grounds out the PU signal atits b contact when the AUTO relay is deenergizcd, indicating transferfrom the automatic governing range. The AUTO relay 72 also controls aswitch 39 that grounds out the answer signal circuit on its a contactwhen the relay is energized and that completes the answer signal circuitthrough its b contact when the relay is deenergized, thus ensuringoperation of the B system as a position servo independently of the Betarange relay when the system is out of the governing range. At this timethe B inputs are the signal '+E at terminal 73 from the b contact of theAUTO switch 71 through switch 67, and the B answer signal through theAUTO switch 89, b contact. The signal +E corresponds to the flight idle(PI) blade angle. These signals will cause the B servo to position atthe flight idle angle when the AUTO relay is deenergized.

Each potentiometer of each servo system is shaped or contoured so thatthe value of the derived voltage at the slider contact bears a desiredrelationship to the angular movement of the contact depending on theparticulm function of the potentiometer, and has a voltage impressedacross its terminals depending as to instantaneous polarity andmagnitude also on the function of the potentiometer. The resistanceelement of the potentiometer may be of the well-known wound card typeand of circular or band form but is diagrammatically illustrated in aplane development for clearness. A structural form of potentiometer thatmay be used in practice is shown by Patent No. 2,431,749 issued December2, 1947 to R. B. Grant.

The contour of all function potentiometers represents the derivative ofthe function concerned and since this involves mathematicalrelationships the potentiometer cards are shown uniform for simplifyingthe disclosure. Specifically, the contour or width variation andtherefore the resistance distribution of a potentiometer is proportionalto the derivative of the function of the characteristic to be simulatedwith respect to the variable represented by the setting of thepotentiometer. For example, let a linear function be assumed as where aderived voltage is to be directly proportional to the distance that thepotentiometer contact is from a zero position. The slope of the functioncurve then is the constant ratio of derived voltage to the increase inthe independent variable represented by the contact travel from the zeroposition. The derivative of this relationship is the same for allcontact settings so that the width of the potentiometer card in thiscase is uniform, making it rectangular in shape. Thus the Width of thecard at any given contact position is determined by the linear ornon-linear character of the function.

Referring again to FIG. 3, the B system output is subject to variouscontrols for simulating conditions incident to operation of the PU andPITCH LOCK relays. The B servo motor control winding 76 is normallyenergized by the output signal from the amplifier 75. However thiswinding may be short-circuited by a shunt connection including theseries-connected switches 90 and 91 when the respective PU and pitchlock relays 92 and 93 are energized. In this condition, a protectingload resistance 94 is connected across the amplifier output and themotor winding 76 is shorted-out to stop the motor for representing apitch lock condition. This circuitry simulates the ratchet operationincident to PITCH LOCK wherein blade angle can be increased but notdecreased under certain conditions as described under PITCH LOCK. Thecontrol of the PU and l0 pitch lock relays 92 and 93 will be laterdescribed in connection with FIGS. 2 and 1 respectively.

The speed response characteristics of the B servo are as previouslyindicated controlled according to feedback. The primary feedback circuitFDBK is permanently connected in the input network to represent thespeed response characteristics when the B system is in the Beta rangeand out-of-feather. When the system is represented as being underacceleration sensitive governing (ATE) control a first shunt circuitFDBK is connected at input terminal 95 across the primary feedbackcircuit by the ATE relay 96 and switch 97 as at its a contact. Thisincreases the amount of negative feedback, resuitin in greater dampingof servo system. When the system is out of ATE control, the relay 96 isdeenergized, FIG. 1, and switch 97 grounds out the first shunt feedbackcircuit at its b contact. A second shunt feedback circuit FDBK is alsoconnected at terminal 98 of the input network across the primaryfeedback circuit by means of the feather relay 99 and switch 100 at itsa contact when the feather relay is energized as later described inconnection with P16. 1. The switch 100 grounds out the second feedbackshunt circuit at its b contact when the feather relay 99 and also thefeather pump relay H31 are deenergized. The relay 101 controls a switchHi2 that grounds out this circuit at its b contact and also ensuresconnection of the shunt circuit at its a contact when the feather pumprelay is energized and the feather relay remains deenergized. Theoperation of the B system under influence of this variable feedbackcontrol will be more fully described in connec tion with the featheringand ATE simulation.

will now be seen that the B servo system is operable with minimumdamping when operating as a position servo in the Beta range underdirect control of the P signal from the power lever, and that when thecontrol is transferred to AUTO, the B system, now operatas anintegrating servo under control of the PU signal, is damped by theadditional feedback introduced by the ATE relay to representacceleration sensitive governor control of blade angle. it will beapparent that damping also occurs when the feedback is increasedincident to shunting in FDBK by energization of the feather relay uponcall for feather. The FDBK damping shunt is also connected in circuitwhen the feather pump relay tut is energized and the feather relay 99 isdeenergized incident to Air Start subsequently described.

When the power lever is advanced for take-off simulation, variouscontrol relays relating to transfer of control to automatic governingare directly affected. Referring again to FIG. 1, when the power lever 2is at T0 position, the governor connect (Gov. Con.) relay it'll? isenergized and the Beta range relay 6 is deenergized by operation of thecams 1G6 and 12 respectively which are positioned by the power lever.The circuit of the governor connect relay is energized from the DC. bus'7 trough the normally closed propeller and engine (P and E) bus tieswitch 8, lead 9, feather motor (Fe. Mot.) circuit breaker lltli', panicswitch 1% that is operable by the panic handle 3, feather switch (FEA.SW.) relay switch in? at its a contact operable by the feather switchrelay lit condition lever switch 111 operable as indicated by thecondition lever and positioned at NORMAL, cam switch 132 at its acontact (or flight (FLT) position), synchronizing switch 113 at SYNCposition controlled by the main synchronizing switch 5 and the relaywinding 1&5 to ground. As the synchronizing switch is normally at SYNC(EG & S) position representing electronic governing and synchronization,and the switches 1 38 and 111 at NORMAL positions, operation of thepower lever cam 1% between the ground (GND) and flight (FLT) positionscontrols the governor connect relay under usual conditions.Concurrently, the power lever cam 12 opens the circuit of the Beta rangerelay 6 by moving the switch 11 from its b contact to the isolated acontact.

The governor connect relay 105 in turn controls energization of theecceleration sensitive electronic governing (ATE) relay 6, FIG. 1,through the switch 114 at its a contact and a series-connected thermalresponsive switch 115 of a thermal delay device 116 connected to the bus7. The thermal delay device 116 comprises a heater element 117 that isnormally energized from the bus through the AC. generator bus tie switch118 so as to cause the switch 115 to warp towards its b contact andclose the circuit. The delay at switch 115 following closing of switch118 simulates the heating time of the electronic equipment representedby the ATE relay. Simulation of failure of the A.C. generator is done bythe instructor opening the switch 118, thereby deenergizing the heater117 which permits the thermal responsive switch 115 to cool and open thecircuit at its h contact.

The ATE relay 96 in turn controls energization of the synchronizing(SYNC) relay 120 through the switch 121 at its a" contact and aseries-connected switch 122 that is connected to the bus 7 andpositioned according to the main synchronizing switch 5. Accordingly,the SYNC relay is deenergized when the ATE relay drops out, representingthe non-governing condition, and also when the SYNC switch is in otherthan the synchronizing position.

Referring briefly to FIG. 3, the propeller under-speed PU signal whichis under control of the AUTO relay 72 and switch 88 is as previouslystated, the principal input signal for the B system when operating inthe automatic governing range. The sense of the signal indicates whetherincreased or decreased B is called for, and the magnitude of the signaldetermines the rate of the B change.

Reference is now made to FIG. 2 for description of the computingcircuitry for deriving the PU signal and for controlling the PU relay92. A summing amplifier 150 for computing PU is fed by an input network151 that may be energized selectively by various signals according todifferent operating conditions, including Beta and automatic governingoperation, feathering, propeller speed and synchronization control. Asindicated, the PU computer 150 represents control for engine No. 1 ofthe four-engine aircraft herein simulated, this engine being normallythe master speed control for the other engines as hereinafter describedunder synchronizing control. 151 is the RPM signal at input terminal 152that is derived from the N servo pot 153. The N servo, which representsthe turbine speed of engine #1 corresponds to the N servo of FIG. 5. Thederived RPM signal at slider 153' represents the instantaneous speed ofthe propeller that is driven through reduction gearing by the turbine.The N servo also controls a cam 154 that operates a switch 155 accordingto certain limits of turbine RPM. When RPM is equal to or greater than4,000, switch 155 engages its a contact so as to connect in circuit aconstant A.C. signal voltage +5, and when RPM is less than 4,000 theswitch engages its b contact so as either to ground the switch circuitor connect with an alternate constant signal voltage +13, depending onthe condition of the feather pump relay 191. Normally, the switch 155 isconnected at its a contact to the aforesaid constant signal source +E.Accordingly assuming now that the control is in the automatic governingrange and that the Beta relay 6 is deenergized, the ATE relay(representing acceleration sensi tive governing is energized and thefeather relay 99 is deenergized, an automatic governing signal +Erepresenting the reference r.p. m. will be applied to the input networkterminal 156 through a circuit comprising the The principal input signalto the network N switch 155, feather relay switch 157 at its b contact,ATE relay switch 158 at its a contact, Beta relay switch 159 at its bcontact, and the usual proportioning input resistance at terminal 156.This +E reference signal is opposite in phase sense to the RPM signal atterminal 15?. so that the resultant or difference signal may be eitherpositive or negative in sense depending on the magnitude of the RPMsignal. This difference signal energizes the PU amplifier which isconnected to an output transformer 160 and the amplified PU signalappearing at the transformer secondary terminal 161 represents thecalled-for RPM change. This PU signal is fed to the B servo system, FIG.3, as previously described.

Operation of the PU relay 92 according to the sense of the PU signal isaccomplished through a phase sensitive rectifier 162 that is connectedto the output of the transformer 160 and to a thyratron 163. The PUsignal from the transformer is thereby converted to DC. dependinginpolarity on the phase sense of the PU signal. The thyratron istriggered to fire and energize the relay 92 when the signal is eitherzero or positive, and to shut off thus deenergizing the relay, when thesignal is negative. Thus, when the summation of the signals at the inputnetwork 151 is zero (which is the normal condition) or of positivesense, the PU relay 92 will be energized, and vice versa.

When the system is represented as being under mechanical governorcontrol, as for example in the Beta range operation, the Beta relay 6 isenergized, the ATE relay deenergized and the constant signal +E appliedto the network terminal 164 through the N switch 155, feather relayswitch 157, lead 165 and Beta switch 166 at its a contact. In thiscondition, the automatic governing circuit at terminal 156 is groundedout by Beta switch 159 at its a contact. Another Beta switch 167connects through its a contact the lead 165 to the network terminal 163so as in this instance to connect the proportioning resistance atterminals 164- and 168 in parallel. This combined signal represents safelimit" operation of engine speed in the Beta range. When control istransferred from the Beta range the aforesaid combined signal isgrounded out at terminal 164 by the series-connected Beta switch 166 andATE switch 169, and at terminal 168 by Beta switch 167, and in placethereof an automatic governing signal is applied at terminal 156; and ifATE control is lost while in the automatic governing range, the ATE andBeta relays are both deener ized and the mechanical governor signalalone is applied through the ATE switch 169 at its b contact and theBeta switch 166 at its 1) contact. It will be assumed of course that thefeather relay 99 is in its normal deenergized position as shown. Whenthe feather relay is energized to indicate call for feathering of thepropeller, the above described circuits at terminals 156, 164 and 168are grounded out, if not already grounded, by the feather switch 157 atits a contact.

An additional signal may be applied to the input network at terminal 17sto represent ,failure of the electric feather pump, i.e. failure ofhydraulic pressure used for feathering. Normally this signal is groundedout by the feather switch 171 at its b contact, or, if at feather, bythe feather pump switch 173, a contact. Assuming now during a call forfeather (energization of feather relay 9%), failure of the feather pumprepresented by concurrent energization of the feather relay anddeenergization of the feather pump relay 101, the feather switch 171 andfeather pump switch 173 now provide from cam switch 155 a signal +E forthe PU input network. This +E signal, through the PU and E systems,causes the resulting P input signal at the N serve, to run this servo tothe 4-269 5:12PM} 12pm. position where {its} it remains thus simulatingloss of the pump which is needed for the completion of feathering.

The control circuits for certain of the relays above referred to willnow be described with reference to PEG. 1. The feather switch (FEA, SW)relay 110 is energized directly from the DC. bus 7 through the conditionlever switch 175 when it is at FEATHER position. in all other positionsof the condition lever the feather switch relay is deenergized. Thisrelay in turn controls through its switch 176 and b contact theenergization of the feather relay subject to control of the torque servo(Q) cam 177 and switch 178. This cam is controlled by the torque servo43 so that the switch is in series through its a contact with the switch1% when torque equals or exceeds a predetermined value, i.e. -l250in.-lbs. If torque goes below this critical value, thus calling forautomatic feathering, the switch 17% engages its b contact so asdirectly to energize the feather relay from the source E through theinstructors Engine Negative Torque Control (ENTC) fail switch 1?).

Normally the cam switch 178 is closed on its a contact indicating normaltorque conditions, and the feather switch relay is deenergized so thatits switch 1'76 engages its normally deencrgized a contact. Thereforenormally the feather relay can be energized only when the relay 110 isenergized in response to call for feather, thus closing the switch 176to engage its energized b contact and complete the circuit for thefeather relay 5 9 through the cam switch 178. In case the simulatedtorque reaches or drops below the critical negative torque valueindicated, the switch 178 transfers the feather relay to an alternatevoltage source without reference to the feather switch relay. Thusautomatic feathering is simulated whenever the torque drops to acritical negative value. if desired, the instructor may move the switch179 to the fail position thus deenergizing the feather relay, it beingassumed that in this case the negative torque is due to malfunctioningof the engine and that the pilot has not yet moved the condition leverto the FEATHER position. in such case the torque will be comeincreasingly negative until a limiting value of -4800 in.-1bs. isreached, at which time propeller and engine wlll be decoupled and torquewill revert to zero as explained in the aforesaid Lem application.

The feather pump relay 101 represents the hydraulic pressure prcduced bythe electric feather pump, which is in addition to a pump driven by theengine. The relay 101i is energized from the bus 7 through the normallyclosed switch 8, circuit breaker 107, panic switch 1%, feather switchrelay switch 1&9 at its b contact (assureing a call for feather and thecondition lever switch 180). The switch 180 is in circuit with the bcontact of switch 3.09 except for the air start (AS) position of thecondition lever. in the air start position, the feather pump relay isenergized directly from the bus through the normally closedcircuit brca(er Hi7 and switch 105, regardless of the position of the eather switchrelay.

The feather timer control (FE TIM CONT) relay 1% is controlled directlyfrom the bus 7 through the panic handle switch 2.82 when moved to thepanic' position. This panic switch also supplies voltage to the acontact of switch 176 so that the feather relay also is automaticallyenergized when the panic handle is thrown to panic position, assumingthe condition lever to be at NOR- MAL. The relay 181 in turn operatesits switch 133 to engage its b contact, thereby automatically energizingthe feather pump relay 101 from the bus when the condition lever is atNORMAL. Thus it will be seen that the feather timer control relayoverrides other controls when the panic handle is thrown for ensuringautomatic operation of the feather pump and feather relays.

The flight idle (Pl) relay The; is controlled according to the operationof the B servo 45. A servo operated cam 135 controls a switch 186 thatis normally closed at its b contact to complete the ground circuit ofthe relay which is directly connected to the bus 7. When the blade angleis represented as less than the flight idle i4 value, the switch 136 isopened and the relay is deenen gized The flight idle relay in turnnormally energizes the automatic governing (AUTO) relay '72 through theswitch Elli? at its a contact thus completing the bus circult to thegrounded relay "72. The AUTO relay is deenergized when the FT relaydrops out in response to B control. An alternate circuit including thePU switch 194 also controls the AUTO relay. This circuit is open whenthe PU relay is energized (for on-speed and underspeed conditions) andis closed on the a contact to energize the AUTO relay for the overspeedcondition.

The pitch locl: relay 93, referred to in FIG. 3, functions to preventovcrspeed and is subject primarily to the control of the N servo 17.This servo operates a pair of cams 1% and 139 for controlling theswitches 190 and 191 respectively. The switch 190 is grounded and openwhen RPM is less than a critical value, i.e., 14,400. The switch 191 isgrounded and open when RPM is less than another critical value, i.e.,14,250. The pitch lock relay, which represents locking of the propellerby a ratchet device arranged so that when the ratchet is engaged theblade angle cannot be decreased but. however, may be increased, isenergized directly from the bus through the grounded switch 190 when RPMis equal to or exceeds 14,400. Further control of the pitch lock reay isprovided by the relay switches $.92 and 1935, the switch 192 engagingits a contact when the relay picks up to complete a holding groundcircuit through the cam switch 191 which is now closed at its a contact.Thus the pitch lock relay is provided with a holding circuit formaintaining it energized between the RPM values of 14,400 and 14 250. Ifhowever the propeller underspeed PU relay 92 is energized indicatingOl1Sp6Cl or a call for increased RPM, i.e. decreased blade angle, thepitch lock relay 93 will remain energized through an alternate holdingground circuit comprising the PU switch 1%, pitch lock switch 193, andits a contact, notwithstanding the fact that RPM may have dropped below14,250. if the PU relay is deenergized calling for decreased RPM(increased blade angle), the PU switch 4 is open and the pitch lockrelay drops out when RPM becomes less than 14,250. This simulates theratchet operation of pitch lock wherein the pitch lock is initiallytriggered by the N servo when RPM exceeds 14,400 and blade angle ismechanically blocked and freezes at that point, subject however torelease of the pitch loch if RPM decreases to less than 14,250 and thegovernor is calling for increased blade angle. If however the overnor iscalling for decreased blade angle (increased RPM) the pitch loclt willremain in ciTect thereby tending to prevent an overspeed condition, asdescribed further under PiT-CH LOQK, FIG. 3.

The one master engine (MA ENG) relay 1% for the simulated multi-enginesystem, further described in FIG. 2, is normally deenergized as thisrelay represents operation of the No. 2 engine as the master speedcontrol. Normally the No. 1 engine is the master control. When howeverthe master control is to be transferred to the No. 2 engine the transferswitch 1% is operated to the ENG 2 position so as to energize the relay195 directly from the bus as indicated.

ENGINE SYNCHRONlZTh-IG CONTROL For a description of the simulatedsynchronizing control. eference is had to FIG. 2. Normally as previouslygrounded a contact, ground out the master engine governor (Ma ENG GOV)signal at the input network 151. That is, there is no synchronizinggoverning signal for the No. 1 engine when it functions as the masterspeed control. The other engines are for brevity diagrammaticallyillustrated by the propeller underspeed PU systems for the respectiveengines. The No. 2 engine is represented by the system PU and the No. 3and No. 4 engines which in the present instance are controlled inidentical manner are represented by duplicate PU systerns designated forconvenience as PU It will be understood that the SYNC relay also isindicated as such for brevity and that an identical relay for the No. 4engine is connected in the same manner to a corresponding PU system alsorepresenting the No. 4 engine.

The N master r.p.m. signal of engine No. -1 is fed to the other enginesystems by means of a potentiometer 202 that is operated by the N servoas indicated. The pot 202 is grounded at a pro-selected mid-portionrepresenting the reference r.p.m. 13,820 corresponding to the setting ofthe electronic governor. The pot is energized at oppositely positionedterminals by constant voltage signals +E and -B so that the voltagederived at slider 202 represents the master engine governor correctionsignal. This correction signal is applied by lead 233 through theparallel connected master engine switches 204 and 205 and the respectivea" contacts thereof, and the corresponding SYNC switches 2% and 207through the respective b contacts thereof to the PU systems of the Nos.2, 3 and 4 engines.

Referring to FIG. 2A which indicates a suitable method of correction, itwill be noted that a constant negative correction signal is applied tothe respective slave engine up to a value approaching the reference-r.p.m. value 13,820. The correction signal is gradually reduced as thereference value is approached in either positive or negative directionin order to avoid overshooting." This application of the correctionsignal is simulated by the arrangement of the resistances 262a and 202bin the potentiometer terminal circuits. The point of connection of theresistance 2432b to an intermediate part of the pot represents the rpm.value at which the negative correction signal reaches its maximum value,the signal at lower r.p.m. values leveling oii and remaining constant.The maximum positive correction signal is determined by the resistance2a and the upper limit of the pot as indicated.

The slave engines are controlled by the No. 1 master engine as aboveindicated in FIGS. 2 and 2A. Primarily, the RPM setting of theelectronic governor is represented by the governor signal +E whichappears at terminal 156 of the Pil input system and at the correspondingterminals of the other PU engine systems for the basic speed control. Ifnow, N should decrease below this setting, a synchronizing signal ofnegative sense will be derived at slider 202' of pot 20-2 and thissignal fed to the corresponding PU systems of the simulated slaveengines, Nos. 2, 3 and 4. The resultant negative signal at therespective PU system input will then in each case produce a correctionsignal +PU (due to amplifier phase reversed) and cause the correspondingblade angle 13;, servo, FIG. 3, to indicate increased blade angle (fordecreasing the rpm.) and the corresponding thyratron to shut-01f therebydeenergizing its respective PU relay indicating an over-speed condition.As the blade angle is increased, the corresponding N system, FIG. 5,receives a signal at its terminal 41 tending to decrease r.p.m. that is,the P signal that is derived in part from B PIG. 4, is decreased so asto decrease the torque function signal for the N servo thereby tendingto decrease r.p.m. and bring it down to the reference N value. Thedecreased r.p.m. signal is then returned to the input network of therespective PU system, FIG. 2, thus completing that part of the servoloop. Synchronization is at- 1h tained when each of the slave servoloops is stabilized at the rpm. of the master engine.

When the master speed control is to be transferred to the No. 2 engine,the Master Engine Synchronizing switch 1%, FIG. 1, is moved to the ENG 2position to energize the master engine relay 195. In this condition themaster engine relay switches 291, 204 and 205, FIG. 2, engage theirrespective b contacts so that the correction signal for the No. 2 engineis grounded out, and the systems for the No. 1 engine and the 'No. 3 andNo. 4- engines each now receive a correction signal from the pot 203 ofthe No. 2 engine servo N the switches 294 and 2555 having cut-out the Nsignal. The N pot 208 is similar to pot 2tl2 so that the derived signalat slider 2%" represents the master engine governor correction signalfor the Nos. 1, 3 and 4 enginesnow operating as the slave engines. Aspreviously stated the SYNC relays of all engines are normally energizedunder electronic governing control, i.e. when the ATE relay 96', FIG. 1,is energized, the ATE relay in turn being controlled by the governorconnect (GOV CON) relay which is normally energized when the power leveris in the governing or flight range.

NORMAL lN-FLIGHT CONTROL Following take-off, normal cruise conditionsare simulated by the normal automatic governing control above describedincident to the pilots adjustment of the power lever within the flightor automatic governing range according to speed and fuel conservationrequirements. The condition lever and the panic handle are both atNORMAL, the Electronic Propeller Governing switch 5 is at SYNC positionand the AUTO and ATE relays are energized. Within the automaticgoverning range, adjustment of the power lever simulates the control ofthe fuel supply to the turbine for producing torque as more fullydescribed in the aforesaid copending Lem application. As the torquesignal from pct 42 of FIG. 5 is increase-d or decreased, the N servo isdirectly affected and tends to respond accordingly to any change in thissignal. The torque signal as noted is a function of both Q and P As theN servo is thus operated in either positive or negative sense, theresulting RPM signal is balanced against the automatic governing signal[E at the PU system, FIG. 2, so as to produce a resultant PU governingsignal depending in sense on whether overspeed or underspeed isindicated and being zero for on-speed. This signal in turn controls thePU relay and the blade angle B servo, FIG. 3. The 13,, servo in turn isused to compute the P signal, FIG. 4, which is fed back as abovedescribed to the N servo. Thus the servo loop is cornplete forrepresenting the dead-beat" characteristic of the propeller controlsystem to be simulated. Simulated synchronization of the four enginestakes place as previously described.

Abnormal in-fiight conditions, such as feathering due tomail-functioning of the engine system, failure of feathering control,etc., may be simulated by means of the apparatus previously described, asummary of which follows.

FEATHERING When simulated engine trouble occurs, feathering isimmediately initiated in order to avoid undesirable windmilling and dragof the propeller. Feathering may be accomplished either by the pilotthrough his condition lever which initiates the feathering action at thefeather switch relay 110, or through his panic handle which causesdirect energization of the feather and feather pump relays, orautomatically through the torque servo when the negative torque due towindmi-lling exceeds a critical value, namely-4250 in.-lbs. If due tofailure of the feather control simulated by movement of the ENTC switch179 to FAIL the negative torque continues to drop to an even greatercritical value, such as4800 in.-lbs., tending to cause a yawing drag onthe aircraft, automatic decoupling of the engine and propeller occurs asdescribed in the aforesaid Lem application so that the negative torqueis within safe limits while the prop is being feathered through thecondition lever. During this operation the Q servo runs to zero,whereupon the engine and propeller are automatically recoupled so thatthe apparatus may be in readiness for an air start.

Assuming now that the pilot has produced feathering through hiscondition lever as above described, the propeller represented by the Bsystem remains at the feather position, i.e. maximum pitch, as long thethe condition lever is positioned at FEATHER. If the condition levershould fail to cause feathering, as by opening of the FE. MOT. circuitbreaker 107, the panic handle may be used. When the panic handle isthrown to PANIC position the feather relay is automatically energizedfrom the bus as above described through the series-connected panicswitch 182 and FE. SW. switch 176, and the governor connect (GOV. CON.)relay which determines ATE control, is deenergized by the panic switch108, thus auto matically transferring the control from ATE to emergencyfeather. This operation of the panic handle also directly energizesthrough the panic switch 182 the feather timing control (FE. TIM. CONT.)relay 181 which, through its switch 183, b contact, energizes thefeather pump relay 101 which is generally energized together with thefeather relay 99 during the feathering operation.

The operation of the B and N servos incident to the feathering operationis controlled by the relays which now are positioned as follows: thefeather and feather pump relays are energized, the GOV. CON. relay isdeenergized with consequent deenergization of the ATE and SYNC relays.Referring now to FIG. 2, the EL. GOV. input at terminal 156 is groundedthrough ATE switch 158, b contact; the MECH. GOV. and SAFE LIM. inputsare grounded through FEA. relay switch 157, a" contact; the FE Pump Failinput is grounded through FE. PUMP relay switch 173, a contact; and theMa. Eng. Gov. input is grounded through the SYNC switch 200, a contact.Accordingly, the sole remaining active input signal RPM at terminal 152now produces an overspeed signal in the PU system which cuts out thethyratron and deenergizes the PU relay and also energizes the B systemat terminal 161, FIG. 3, so as to increase B toward feather, andconsequently reduce the P signal so as to in turn reduce rpm. at the Nservo.

When the PU relay drops out, FIG. 1, the alternate circuit for the AUTOrelay is closed through switch 194 ensuring energization of this relayto allow feathering from the Flight Idle blade angle. Referring now toFIG. 3, the +FI STOP input is grounded through AUTO switch 71, acontact; the +P input remains grounded through B range switch 66, acontact; and the ANS input is grounded through AUTO switch 89, acontact. The remaining input signal :PU, which corresponds to theoverspeed PU signal above referred to, is fed through the AUTO switch88, a contact, to drive the B servo toward maximum blade angle, i.e.feather. As the B servo runs toward feather, the P signal which isderived from the B pots 140 and 142, FIG. 4 is accordingly decreasedtoward its minimum value.

Referring to the N system, FIG. 5, the active input signals are now theV effect at terminal 43 and the torque signal (derived from the Q servoand the aforesaid P signal) at terminal 41. As the P signal decreaseswith increased B and the Q signal decreases due to fuel cut-off, the Nservo under the reduced torque signal runs down toward lower r.p.m.under influence of its answer pot 22; also the derived V eflect" signalat pot '44 is gradually reduced toward zero as the slider 44' is movedtoward the upper grounded position representing maximum B or feather,thus reducing the re- 18 sultant input signal at the N servo to aminimum value and causing the N servo to position accordingly. Thepropeller system is now represented as being feathered and at minimum orzero r.p.m.

If on a call for emergency feathering for any reason, the electricfeather pump should fail, feathering is partially completed by theengine-driven oil pump so as to cause r.p.m. to drop to about 4200 whereit remains constant. At this r.p.m. there is insufficient pump pressureto produce further feathering. This operation is simulated by feeding aFEA. PUMP FAIL signal +E from switch 155, FIG. 2, to the PU inputterminal through the series-connected feather pump and feather relayswitches 173 and 171. As this signal is less than the -RPM signal, theresultant input signal is negative, an overspeed condition is indicatedby the PU output signal and B is increased toward feather. This causesthe N servo to run down until rpm. is about 4200, at which point the PUgoverning signal is zero and the B servo indicates a fixed pitch, thussimulating the limit of feathering by the engine-driven pump. Allfeathering operations take place as above described when the electricfeather pump is lost.

Referring again to FIG. 5, the engine shaft r.p.m. system, representedby N, is shown as being energized primarily by the aforesaid activeinput signals. These are essentially three main torque or force signals,canstituting the engine torque (Q) and propeller load torque (P signalscombined at input junction 41, and the V efiect 0r wind-milling torque(which depends on blande angle [3 and air speed V signal at inputjunction 43. Accordingly the indicated shaft r.p.m. is determineddirectly by the above three torque signals, depending on the magnitudeand sense of the respective signals.

AIR START As above indicated prerequisites for the air start are thatthe propeller be at feather and of course the propeller and engine unitsnormally coupled. As the torque at feather is zero, the units will beassumed coupled and the turbine r.p.m. at zero. Air start is initiatedby moving the condition lever to the AIR START position, thereby openingthe condition lever switch 111 to ensure deenergization of the governorconnect relay 105, and hence the ATE and SYNC relays 96 and 120respectively, and closing the condition lever switch at its AS contactto energize the feather pump relay 101. The power lever is positioned atits flight idle FI position thereby maintaining the cams 12 and 106 atthe FLIGHT position thus ensuring deenergization of the Beta rangerelay, FIG. 1. The panic handle is of course returned to its NOMALposition so that the feather relay is now deenergized. As the bladeangle is greater than the FI value, the AUTO relay will be energizedthrough the FI relay.

With energization of the feather pump relay 101, FIG. 2, and with therpm. now less than 4000 a MECH. GOV. signal +E is fed to the PU inputterminal 164 through the FE. PUMP switch 172, a contact, N cam switch155, b contact, FEA. switch 157, b contact, ATE switch 169, b contact,and Beta switch 166, b contact. As above indicated, the other inputs aregrounded out except for the --RPM signal which is zero. Accordingly, theresultant input signal is +E which produces a large underspeed signal atthe PU output, thereby picking up the PU relay. This signal alsoenergizes the B servo through the AUTO switch 88, a contact, so as todecrease blade angle and bring the propeller out of feather, the otherprimary signals including the -ANS signal being grounded out so that theB servo now integrating, runs toward lower pitch under influence of thePU signal. During this operation, the B servo is damped a certain amountby the shunt feedback FDBK that is connected in circuit by the featherpump switch 102 to simulate the un-feathering rate.

Referring now toFIG. it will be seenth'at as B, decreases, the V effectsignal from: pot 44. is increased, thus *simulating-the windmillingtorque. tending to drive the turbine. Accordingly, the N servo. runsupward from its zero position toward a value at which the FLAME: relaymay be assumed energized,- the Q. servo operating and the servo nowrunning. up to normal speed. under influence of the torque signahfromipot 42'.

When the. air start has. been accomplished (evidenced 3 Feather a iiiiiii. E E 'ergized y PITCH? LOCK above indicated; pitch lock isfreezing; of: the blade angle at a critical r.p.rn. so as to prevent anyfurther r.p.m. increase that otherwise might occur if B were decreased.Normally the pitchl'o'ek -relay is' de'energized, FIG; 3, sorthat itsswitch 91 perm-its normal functioning-, of the B motor winding '76. 'Ihcconditions -for energization of the pitch lock relay 93 have previouslybeenexplainedint-connection with-FIG. 1'. Summarizingbriefly;.the-relay'is'picked up when r:p.m. reaches 14,400 and: islocked in by. a holding'circuit that is" effective until rpLm. dropsbelow 14,250; also an alternate holding circuit for the pitch lockrelay/ is effectivein case the PU relay. 92 is energized, ire.indicating underspeed with call for decreased'pitch. Thus the pitchlock'relay can be deenerg-ized only. when: the PU relay: drops outto indi-'cate call: for increased pitch and r'.p.m. drops below" and thus reducer.p.m. to-=the point where the pitch locle relayalso drops out. Thuswithpitch loc in effect, the B sewocan increase blade angle to reducer.'p.m.

but it: cannot enhance the: overspeed condition by de-' creasing theblade -angle,.thereby simulating mechanical ratchet; operation forpitchv lock.

LANDING When landing'is to be simulated, the power lever is" retarded-toflightidleOFI) position which causes' the-Q servo; to-run down, thetorque signal to decrease, FIG. 5, andthe N servo to run down to anunderspeed npm.

The B servo under influence. of the; PU underspe'ed signal then runstoward lower pitch unitl N is stabilized at on-speed. If a blade angle:lowerthanthe F-I'value' 75'v lever to the automatic governing ATEcontrol. This (a-bout'9"). is called for, B isiblbcked mechanically atthis limiting value in the aircratt.- This is simulated by the Bcontrolled FI-relay='184, FIG. 1, which drops out the AUTO relay'at'theFI value thus stopping the nor-' mal governing operation.

Referring now to FIG. 3, it will be seen that AUTO switch. 71inserieswith Beta switch-67 feeds to the B,

servo-a signal +E representing the flight idle stop angle The normal PUinput is now grounded out by AUTO switch 88", so. that the. B servofunctions through its answer circuit (switches 89and 69') to position atthe F1 angle Assuming now that the power lever'is subsequently ad vancedsomewhat above the FI position on a call for more power, the resulting Qincrease. causes r.p.m. toincrease, FIG. 5 and PU to indicate overspeed,FIG. 2, re-

sults' in the. PU relay 92dropping out and the AUTO relay. to be.energized through its alternate circuit, FIG. 1.- This cuts out the FIstop signal and reconnects' the PU input to the- B servo so as increaseB thus returning the system to normal governingoperation.

Summarizing, the FI STOP signal that is introduced inplace of the PUsignal when the power lever is retarded to its FI position, causes the Bservo to run down to its,- FI' value. whe'reit is stabilized to'block"further decrease However, by reason of the PU and of blade angle. AUTOrelays, the F1 STOP signal'may be. cutout to restore the PU signalandthus permit increase of blade angle. on a call for m'ore'power; ifsuch is needed.

When the simulated flight reaches ground, thepower lever isfurther.retarded so that it is now in the'Beta or ground range wherein the cams12 and 106 arepositioned. to close the respective switches 11 and 112"at GND, FIG. 1, automatic governing control iscut out the Beta relay isenergizedand blade angle-control is directly: subject'toxthepower lever,FIG-3'. In thiscondition thel Bpservotnow a position servo) can be rundown toward flat-pitch under control of'theP-L signal toreduce' forwardthrust, and desired can be further run to reverse pitch toproduce-reverse or braking thrust.

A secondary effect of reverse thrust is simulatedby means ofthe B pot44, FIG. 5, that is grounded ata of negative sense'is fed to the'Nservo, thus opposing the torque signal from pot 42 andtending to reducerpm. However, r.p.rn. remains substantially constant by reason of thescheduled fuel how in the-Beta ran-geas described-in the aforesaid Lemapplication.

MECHANICAL GOVERNOR AND SAFE LIMIT CONTROL Referringrto FIG; 2,themechanical governor (MECH'L GOV.) signal +03 from theN cam switch maybeapplied under both ground 'and flight conditions of the- Betarelay 6,depending on the automatic governing ATE relay, assuming that rpm. is:greater than 4,000which is usually the case. Thatds... if ATE control islost in flight, the ATE inputis grounded and the MECHLGOV. signal isthen automatically fed through the ATE and Beta: relay. switches 169 and166 respectively. to the PU input terminal 164. This signal represents.man. of about. 13,600 and governs'the-PU' system accordingly in theabsence of the ATE control.

When operating solely in the. Beta or ground-range an additional SAFELIMIT signal is applied to the PU 21 SAFE LIMIT input at the PU terminal168 is conveniently connected in parallel with the MECI-I. GOV. input soas to be energized by the aforesaid +E signal. In the flight range theSAFE LIMIT input is unnecessary and is grounded out by the Beta switch167.

SYSTEM SHUT DOWN When the system is to be shut down after landing, thecondition lever is moved to GND STOP, the power lever remaining at theground idle position within the Beta range and the B servo being at fiatpitch under control the PL signal. The propeller control is not affectedwhen the condition lever is moved to GND STOP, as NORMAL controlcontinues in effect. However, the engine fuel supply is shut off so thatthe Q servo runs to zero (as described in the aforesaid Lem application)which in turn causes the N servo also to run to zero, thereby simulatingcomplete engine shut down.

SYSTEM FAIL CONTROLS In the aircraft, certain circuit breakers areconnected in the electrical system for overload protection and when theytrip open produce various conditions affecting the propeller control.Referring to FIG. 1, these conditions are simulated by means of a numberof circuit breakers indicated as connected in the circuits of certainkey or principal relays. These circuit breakers are normally closed tocomplete the respective circuits and are opened under simulated overloadconditions, malfunctioning of the electrical system, etc.

Referring first to the master synchronizing (Ma SYNC) circuit breaker197, opening of this breaker simply deenergizes the Ma ENG relay 195(assuming that the synchronizing control is under the No. 2 engine),with the result that the synchronizing control is automaticallytransferred back to the No. 1 engine.

The feather motor (PE MOT) circuit breaker 1&7 affects the FEA PUMPrelay 101 and the GOV. CON. relay 105 which in turn controls the ATE andSYNC relays. Accordingly when the FE MOT circuit breaker 107 is openedthe GOV. CON. relay is deenergized and both ATE and SYNC controls arelost and the system is automatically transferred back to mechanicalgoverning control as above described. Closing of the FE MOT circuitbreaker restores the ATE and SYNC controls. The Fea PUMP relay is notnecessarily lost when circuit breaker 107 opens and may be energizedthrough an alternate circuit under control of the panic handle aspresently described.

The emergency feather timer (Em Fe Tim) circuit breaker 198 affects theaforesaid alternate circuit, i.e. the panic handle control circuit forthe FEA PUMP relay 101. This alternate circuit is effective only whenthe panic handle is thrown to energize the feather timer control relay181. Thus, opening of circuit breaker 198 prevents panic operation ofthe feather pump. The normal control circuit for the FEA PUMP relay 1111is through the feather switch relay contact -9 under control of thecondition lever. Accordingly if both the Fe MOT circuit Jreaker 107 andthe Em Fe Tim circuit breaker 198 trip open at the same time, the FEAPUMP relay cannot be energized, thus simulating inability to use theelectric feather pump while the circuit breaker is open.

The emergency feather circuit breaker 199 affects both the Fe Tim Contrelay 81 and the feather relay 99 for panic handle control. That is, thefeather pump relay and the feather relay cannot be energized through thepanic handle when the circuit breaker 199 is out. However, alternatecircuits as above described may be available for energizing these relaysunder control of the condition lever if the circuit breaker 199 shouldopen. Thus the effects of opening the aircrafts overload protectioncircuit breakers for the propeller control system are simulated by meansof switches in the circuitry of the principal control relays.

It should be understood that this invention is not limited to specificdetails of construction and arrangement thereof herein illustrated, andthat changes and modifications may occur to one skilled in the artwithout departing from the spirit of the invention.

What is claimed is:

1. Flight training apparatus for simulating the propeller system ofturbo-propeller aircraft having a simulated power lever movable throughcontrol ranges represent ing ground and flight conditions, respectively,and turbine torque computing means, comprising simulated propeller loadcomputing means, an electrical computing system representing turbiner.p.m. responsive to a torque signal that is produced by said torquecomputing means jointly with a propeller load signal that is produced bysaid propeller load computing means, a second electrical computingsystem representing automatic governing control jointly responsive to asignal representing turbine r.p.m. from the rpm. system and a signalrepresenting a reference rpm. for in turn producing a simulated rpm.overspeed or underspeed error signal, a third electrical computingsystem representing propeller blade angle responsive to said errorsignal for adjusting simulated blade angle, the aforesaid propeller loadcomputing means being responsive to a signal representing propellerblade angle from the blade angle computing system for computing thesimulated propeller load, and means controlled by the power lever foralternative control of said third system so that said system iscontrolled by manual operation of said power lever in the ground rangethereof, and is controlled by said error signal when the power Elevel]lever is in the flight range.

2. Flight training apparatus as specified in claim 1 having a firstrelay means adapted to be controlled according to the overspeed orunderspeed sense of the automatic governing signal, a second relay meansrepresenting automatic governing adapted to be controlled by the bladeangle system when said system is at a position representing the bladeangle as exceeding flight idle blade angle, said first relay means whenunder control of an overspeed signal adapted to control the automaticgoverning relay when blade angle is represented as at flight idle orless, so that said governing relay is in condition for simulatedautomatic governing control of the blade angle system at less than theflight idle value.

3. Flight training apparatus as specified in claim 1 having means forsimulating the propeller flight idle angle stop comprising switchingmeans for applying a constant signal to the blade angle system, saidswitching means being controlled by the power lever in the flight rangethereof and according to the simulated automatic governing control inthe non-governing position thereof jointly to apply said signal.

4. Flight training apparatus as specified in claim 1 having signalderiving means operable by the power lever, and relay means controlledby the power lever in the ground range thereof for applying according tothe position of the power lever a derived signal to the blade anglesystem for simulating direct control of blade angle by the power leverfor groun operation.

5. Flight training apparatus as specified in claim 1 wherein the bladeangle system is a servo motor system alternatively operable as anintegrating and position servo, and switching means controlled accordingto the position of the power lever and according to the sense of thesimulated automatic governing control for causing the blade angle servoto function as a position servo when the power lever is in the groundrange and also when the power lever is in the flight range and theautomatic governing control is in the non-governing position, and

as an integrating servo when the power lever is in the flight range andthe governing control is in the governing position wherein the automaticgoverning signal controls the blade angle servo. I

6: Apparatus-specified in claim l having relay means controlledaccording tothe respective operating ranges ofthevpo'wer lever forselectively applying the automatic governing error signal tothe thirdelectrical computingsystem representing'propeller blade angle when thepower lever is in the flight range, and for applying a signal accordingto the position-of the power lever representing manual-control of: theblade anglewhenthe power lever is; in the: groundrange.

7. Flight training. apparatus as specified in claim I having; computingmeans for producing a signal-representing air: density, wherein the.propeller blade angle computing. means is; also responsive. to-turbinerpm. and air density signals;

8.-Flighttraining. apparatus as. specified in claim 1 whereinthe meansfor producing the automatic governing. signal comprises" an. electricalsystem having an input-network energized by the rpm. signal andalternatively' by signalsrepresenting respectively electronicacoeleration sensitive governing and mechanical governing, andmeansundercontrol of the-pilot for selectively. applying the: alternativesignals:- according to. the simulated senting a correction et'ron'withrespect to a reference rtpmrrepresentingathe setting of the electronicgovernor,

andmeans controlled by' said selecting Y means. for applying s'aid errorsignal tothef respective networks of the other duplicate apparatus forproducing governing signets tending-.16 rtiai'ntain all duplicateapparatus at simulatedsynchronous r.p .m.'. with respect to theselectedapparatus.

1 1-. Flight training apparatus 'as specified in claim 8' having relaymeans adapted to becontr'olled when the power 'leveris' -in the ground'ra-ngefo'r applying signals representing -mechanical-- governing andsafe r'.p-.m. limit respectively to the network, said relay meansbeingcontrolled s'o as are in an' alternate position when the powerlever is -m-the flight rang'e, ase'cond relay means adapteo te beeommllem when'the. condition lever is at normaWand the first namedrelaymeans under flight control for cutting out said mechanical governingands'a'fe-hinit signals and E for applying a signal representingelectronic govemingto the network; both said" relay means beinginterrelated so that if'thesecond relay means:

is in a controlposition representing loss of the simulated' electronicgoverning control withthe resultant cutting out of the -'electronicgoverning signal the mechanical g'overning-signal is! applied jointly byboth said relay means to the -n etwol'k.

1 2; Flighttraining apparatus as specified in claim 8 wherein' the meansunder control of the pilot comprises a condition lever movable topositions representing air stars normalt and feather and the aforesaidpower leverg said condition-lever in the normal positionthereofeoincident"with'the powerlvcr-in the flight range"controllingmeans for selectively applying to the network the electronicgoverning signal, and said power lever in the ground range thereofcontrolling means for cutting 'out theelectronic governing signal andapplying the mechanical governing signal.

13. Flight training' apparatus asspecified in claim 12 having meanscontrolled by the condition lever at the feather position thereof forcutting" outthe electronic and: mechanical; governing signals so that"the: automatic governing signal resulting from: the: dominant r.p.m.

signal represents an overspeed condition, said overspeed governingsignal energizing theblade angle system so as:

to operate said system toan increased blade angle position representing;feather.

14. Flight training apparatus as specified in claim 13 having meansrepresenting an electric feather pump for applying a signal to theautomatic governing input n twork for representing failure" of theelectric feather pump, coincident with pOsitiOning of the conditionlever at feather, the resulting governing signal causing the blade anglesystem to run to an intermediate blade angleposition and the r.p.m.system to run to a low speed indication thereby simulating partialfeathering by the engine oil pump upon failure of the electric featherump.

15. Flight training apparatus as specified in claim 1 having means forapplying a signal representing starter torque to the turbine r.p.m.system undercontrol of the rpm. system and means for applying anadditional signal representing added torque due to simulated firing 0fthe turbine.

16. Flight training apparatus as specified in claim 15 having. meanscontrolled jointly by the blade angle system and by asignal representingairs'peedfor producing. and applying to the rpm. system a' signalrepresenting the airspeed eifect-on the propeller rpm.

17. system for electrically simulating the operation of a'propellerpitchlock system having a rotatable device subject to' on-oif mechanicalratchet control'wherein the ratchet is made effective toblockrotationand corresponding blade. angle change in one direction andto permit rotation in the opposite preferred direction andalternatively, to be made ineifective thereby permitting.

other, a pair of relays having interrelated switchingT means forselectively deenergizing; said control winding so as to lock said servomotor in position; and for ener gizing said winding to rotate the motorinsaidpreferred direction, one of said relays being controlled accordingto a simulated-propeller pitchlock-condition, and the other lrelay beingcontrolled. according to the sense ofthe motor direction signal forpermitting operation of the motor only in the'preferred direction duringsimulated pitch lock.

18. A system for electrically simulating the operation of a rotatabledevice subject to mechanicalrratchet controlwherein the ratchet isoperable selectively to block rotation in but one direction, to permitrotation in either direction and to block; rotation in both directions,comprismg a reversible electric motor representing said ro-' tata-bledevice and having a control winding; a relay switching system forselectively controlling. according to a plurality of simulatedconditionsthev sense of energization of said winding, and for blocking rotation ofsaid motor, said system including means jointly responsive to amotonwinding input signal of predetermined sense representing one ofsaid conditions and a signal representmg another condition forpermitting rotation in but one direction, said other condition signalwhen of opposite sense controlling said means for pcrmitting'rotation nalternate directions, said means being responsive: ointly to said lastnamed condition signal and to the input signal of sense opposite tosaidpredeterminedsense for blockingrotation of said motornotwithstanding. application of motor input signals.

19. In electrical apparatus for simulating theperformance'o-f aircrafthaving an engine pr'opelle r combination, means for computingandindz'catir'tgpropeller shaft" r.p.m. comprising a system forcomputing and pro'ducinga signal representing. the magnitude and senseofengine torque senting propeller blade angle responsive to simulatedpower demand, a third system for representing propeller shaft r.p.m.,means responsive to joint operation of the blade angle and r.p.m.systems for producing a signal representing the magnitude and sense ofpropeller load torque acting on said shaft, a source of simulatedaerodynamic factor signals and means controlled by said blade anglesystem and simulated aerodynamic factor signals for producing a signalrepresenting the magnitude and sense of torque acting on said shaft dueto propeller wind-milling effect, said r.p.m. system being jointlycontrolled by the aforesaid three torque signals for computing andindicating propeller shaft r.p.m.

20. Apparatus as specified in claim 1 9 having a simulated power controllever and a simulated fuel flow system responsive to positioning of saidlever by the pilot, the torque computing system being responsive jointlyto the operation of said fuel flow system and the r.p.m. system.

21. Apparatus as specified in claim 19 wherein the r.p.m. systemcomprises an electric servo motor system that is subject to change inposition and indication according to the magnitude and sense of theresultant of the three torque signals.

22. Apparatus as specified in claim 21 wherein the r.p.m. and bladeangle systems have signal producing means and the signals therefrominterrelate said systems so as to adjust the r.p.m. servo positionaccording to simulated blade angle.

23. In electrical analog apparatus for simulating the performance ofaircraft having an engine-propeller combination, means for computing andindicating propeller shaft r.p.m. comprising an electric servo motorsystem having a shaft and r.p.m. indicator for representing r.p.m.according to angular positioning of said shaft, an electric servo motorsystem also having a shaft that is angularly positioned according tosimulated blade angle, a source of signals that are representative ofsimulated aerodynamic and flight factors, means for producing a signalrepresenting simulated engine torque, means for producing a signalrepresenting propeller load torque according to joint positioning ofsaid r.p.m. and blade angle servo systems and to the magnitude of anaforesaid factor signal, and means for producing a signal representingwindmilling torque acting on the propeller shaft according topositioning of said blade angle servo and to the magnitude of anaforesaid factor signal, said r.p.m. system being responsive to theresultant of said three torque signals for positioning the servo shaftto indicate propeller r.p.m.

24. In electrical apparatus for simulating the performance of aircrafthaving an engine-propeller combination, means for computing andindicating propeller shaft r.p.m. comprising interrelated andinteracting propeller blade angle and propeller shaft r.p.m. servo motorsystems, a source of signals representing a function of true airspeed,said servo systems in combination with said function signal beingadapted to produce signals representing respectively propeller loadtorque and propeller wind-milling torque, means for producing a signalrepresenting engine output torque, said r.p.m. servo system beingjointly responsive to the resultant of said torque signals forpositioning the servo to represent propeller r.p.m.

References Cited in the file of this patent or the origlnal patentUNITED STATES PATENTS 1,960,350 Shackleton et a1 May 29, 1934 2,397,477Kellogg Apr. 2, 1946 2,506,949 Bu rlebach May 9, 1950 2,608,005 KennedyAug. 26, 1952 2,788,589 Stern Apr. 16, 1957 2,798,308 Stern et a1 July9, 1957 2,804,698 Grandmont Sept. 3, 1957 2,824,388 Stern et a1. Feb.25, 1958

